Scalene muscles are accessory respiratory muscles that originate from the neck vertebra and terminate on the first rib.

While there are three scalene muscles: the anterior scalene (in front), the middle scalene, and the posterior scalene (in back); the anterior and middle scalene muscles are primarily involved in thoracic outlet syndrome.

The subclavian vein traverses the thoracic outlet over the top of the first rib and in front of the anterior scalene muscle.

The subclavian artery and the brachial plexus traverse the thoracic outlet over the top of the first rib and in the space between the anterior and middle scalene muscles.

To complicate matters even further, it is very common for the scalene muscle fibers to actually weave in and around the nerves and artery within the space between the anterior and middle scalene muscles.

An abnormal dynamic between the scalene muscles and the first rib, causing compression of the adjacent neurovascular structures leads to the distinct symptom complex of TOS.

Abnormal scalene muscle spasm compresses the neurovascular structures between the muscles groups as well as the first rib.

This scissoring effect of the muscles against the neurovascular structures leads to a chronic crush injury and the development of symptoms.

Arterial or venous compression alone is thought to each account for 2-3% of all thoracic outlet syndrome cases.

The remaining 95% of TOS is caused by either nerve compression alone (pure neurogenic) or nerve and arterial compression combined (mixed neurogenic).

Rudimentary or cervical ribs, extending from the seventh cervical vertebrae, can also contribute to the development of TOS.

These extra ribs or associated cartilage bands can act as additional structures against which neurovascular structures can be pinched.

Cervical ribs occur in up to 1.5% of the normal population and are found more often in women.

Patients with cervical ribs have them on both sides 70% of the time.

When cervical ribs are present, they are most commonly associated with symptomatic arterial compression.

The most common cause of thoracic outlet syndrome is trauma.

Injuries that produce flexion/extension injuries of the neck (i.e. whiplash), or repetitive use/overuse are responsible for the vast majority of cases.

Contributing factors such as sagging shoulders, large breasts, a narrow scalene triangle, and a high take off of the nerve bundle within the scalene triangle may explain why some individuals are more prone to developing symptoms of TOS.

Pain is the most common presenting symptom in patients with neurogenic thoracic outlet syndrome.

It may be located in the neck, shoulder, arm, forearm, hand, or chest (front or back).

Up to 75% of patients will also complain of headaches.

Vascular symptoms from arterial or mixed TOS include coolness or color changes in the hand, arm fatigue, or in severe cases of isolated arterial TOS- ulcers or gangrene.

Nerve symptoms are primarily related to compression of the brachial plexus as it traverses the region of the first rib.

Classically, patients with TOS complain of numbness and tingling corresponding to the area the fourth and fifth digits.

Thoracic outlet syndrome is a clinical diagnosis, meaning it is based primarily on the clinical symptoms and physical abnormalities found by the examining physician.

Key findings may include tenderness, pain, or numbness in the arm or hand when palpating over the scalene muscles.

Having the patient hold their arms in positions that close off the thoracic outlet will typically produce a loss of pulse at the wrist and symptoms of numbness, tingling, or pain in the arm or hand.

TOS patients who do not respond to the above types of treatment are typically referred for surgical consultation.

Surgical treatment is designed to relieve compression at the thoracic outlet and create more space in this area.

This is achieved by releasing the scalene muscles from the first rib (surgically cutting them or partially removing them), removing the first rib in the area of the neurovascular structures, clearing the neurovascular structures from any other constructing bands of muscle or fibrous tissue, and removing any accessory or cervical ribs.

In well selected patients, the results of TOS surgery are quite good, with most patients reaching approximately 85% of their pre-injury functional state.

At EvergreenHealth Heart & Vascular Care, we are recognized as one of the state’s leading experts in the surgical management of TOS.